The present invention relates to an oil-lubricated scroll-type fluid machine suitable for use as a refrigerant compressor for an air conditioner or a refrigerator, as well as an air compressor and, more particularly, to a scroll-type fluid machine in which a predetermined clearance is intentionally formed between the side surfaces of wraps of a stationary scroll member and an orbiting scroll member.
In, for example, U.S. Pat. No. 4,082,484 a scroll-type machine, serving as a compressor, is proposed which includes a stationary scroll member and an orbiting scroll member each of which has an end plate and a wrap formed along an involute curve or a curve simulating an involute curve so as to extend upright from one side of the end plate. The scroll members are assembled together in a housing such that the wraps thereof mesh each other, with a suction port and a discharge port formed in a central portion and a peripheral portion of the end plate of the stationary scroll member and communicating with a suction pipe and a discharge pipe connected to the housing, respectively.
An Oldham's ring adapted, for preventing the orbiting scroll member from rotating about its own axis, is disposed between the orbiting scroll member and the frame of the machine or the stationary scroll member. The orbiting scroll member is driven by a main shaft engaging therewith, so as to execute an orbiting movement with respect to the stationary scroll member without rotating about its own axis, such that the volumes of closed chambers formed between the wraps of two scroll members are progressively decreased, thereby compressing a gas confined in these chambers and discharging the compressed gas from the discharge port.
From the view point of minimization of wear or abrasion the wrap side surfaces, it is desirable that a minute clearance be maintained between the opposing side surfaces of the wraps of both scroll members, i.e., that the opposing side surfaces of the wraps of both scroll members do not directly contact each other, during the operation of the compressor.
If the scroll members are precisely machined in conformity with the theoretical design, the orbiting scroll member will make an ideal orbiting movement on a circle of a radius conforming with the theoretical radius without making any vertical oscillation, so that undesirable axial displacement of the orbiting scroll member, which may result from an inclination of the orbiting scroll member is advantageously avoided.
Actually, however, different phases of the scroll members provide different sizes of radial clearance between the wraps of both scroll members because of tolerances in machining of the scroll members.
During the operation of the scroll compressor, a force is generated by the pressure of the gas under compression in the compression chambers formed between the stationary scroll member and the orbiting scroll member. This force is divided into an axial force component which tends to separate the orbiting scroll member downwardly from the orbiting scroll member and a radial component which resists the driving torque exerted by the main shaft. On the other hand, a counter force which balances the radial component is exerted on the eccentric shaft portion of the driving main shaft so as to act in the direction opposite to the radial component. On the other hand, an intermediate gas pressure, established in a back pressure chamber formed behind the orbiting scroll member, generates a force acting on the rear side of the orbiting scroll member. Consequently, a moment of force is generated due to a discordance between the point of application of the radial component and the point of application of the counter force.
During the operation of the scroll compressor, the moment of force causes an inclination of the orbiting scroll member, allowing a mutual contact between the wraps of both scroll members resulting in a rapid wear of the wraps or, in the worst case, a breakdown of the wraps of both scroll members.
In order to avoid the occurrence of an undesirable inclination of the orbiting scroll member, in, for example, Japanese Patent Laid-Open No. 110887, the axial clearance at the outer periphery of the end plate of the orbiting scroll member is so determined as to avoid any local contact between the end surface of the eccentric shaft portion of the driving main shaft and the orbiting bearing receiving this eccentric shaft portion. Thus, in this prior art, the radial clearance at the peripheral portion of the end plate of the orbiting scroll member is regulated with respect to the outside diameter of the end plate of the orbiting scroll member, clearance in the orbiting bearing and the length of the orbiting bearing.